1. Field of the Invention
This invention relates to a high-performance, low-profile tire for four-wheeled passenger car having an aspect ratio of 35–55%, and more particularly to a tire wherein the rise of the vertical spring constant of the tire is suppressed and the lateral spring constant thereof is properly raised to improve the steering stability in the high-speed cornering and also the peripheral length in the ground contact face of the tire is ensured to maintain the ground contacting property to thereby improve the traction transmitting force (acceleration performance).
2. Related Art
Recently, it is strongly demanded to improve the steering performances of the tire, particularly the steering stability accompanied with the advance of the performances in the vehicle.
As a low-profile radial tire for a passenger car having an aspect ratio H/W of tire section height H to tire maximum width W of not more than 0.60, there is known a tire structure improving the steering performances that a carcass is comprised of a carcass cord ply having a main body portion and a turnup portion connecting with the main body portion and wound around a bead core from an inside of the tire toward an outside thereof and a carcass cord ply consisting of only a main body portion terminated outside the above carcass cord ply without winding around the bead core and a spacer rubber is interposed between the main body portions of the two carcass cord plies in a zone ranging from an axially outer end of a belt to a maximum width position being a maximum width of the tire to form a ply-separating portion in which a distance between cords of the adjoining main body portions is 0.55–5.5 times of a cord diameter (see JP-A-2002-67616).
In such a conventional low-profile tire, it is said that since the ply-separating portion is formed between the adjoining carcass cord plies in the zone ranging from the outer end portion of the belt to the tire maximum width position, it is possible to improve the steering performances and also the tire weight can be reduced.
However, this tire has a problem that the absorbability of vibrations input from a road surface is low and the steering stability in the high-speed cornering (road holding property) is poor because a flex zone in the vicinity of the carcass shoulder is excessively reinforced accompanied with the reinforcement of the zone ranging from a bead portion to a side portion.